1. Technical Field
The present invention refers to an accelerated and environmentally advantageous process for nixtamalization of corn for the preparation of tortillas, tortilla chips, corn chips, and the like. The invention uses specific processing steps to process ground corn fractions and/or ground whole corn as a substitute for the traditional nixtamalization process.
2. Description of Related Art
Corn was the principal source of food for the pre-Columbian civilizations of the New World. Today corn tortillas and derivative products are still the staple food of Mexico and Central America. Also, corn tortilla, corn chips, and tortilla chips have widely penetrated the market of the United States and some countries of Asia and Europe.
Nixtamalization, also known as alkaline cooking, is the traditional process for making corn masa used as the base ingredient for many Mexican-style corn products, such as corn tortillas, tortilla chips, taco shells, tostadas, tamales, and corn chips. It is believed that ancient Central Americans cooked maize in a dispersion of wood ashes or lime to produce corn tortillas, their major form of bread. This ancient technique, having undergone little changes, still involves cooking and steeping whole kernel corn in a solution of lime (calcium hydroxide). Nixtamalization transforms corn so it can be stone ground to form dough called masa that is subsequently sheeted, formed and cut in preparation of tortillas and related snack or food products.
The traditional method to process corn into tortillas (nixtamalization) goes back to early Mesoamerican civilizations, and the basic steps of the process have remained basically unaltered since. In the traditional process, whole corn is cooked in a boiling water-lime (or water-ash) solution for a short time (5-45 min) and steeped in this solution, as it cools, for a period of 12 to 18 hours. The cooking liquor, called nejayote, is discarded; the fraction of the pericarp and germ dissolved in the nejayote is lost. The cooked, steeped, and drained corn grains (nixtamal) are washed to remove excess lime. Here again, a part of pericarp and germ material is lost. The total corn fraction lost varies from 5 to 15%. The highly alkaline (pH 11-12) nejayote, is rich in corn solids and excess lime and is a waste product of both traditional nixtamalization and instant masa flour production. The nixtamal is ground with a pestle and stone into masa. Finally, the masa is flattened into thin disks that are cooked on a hot griddle for 30-60 seconds on each side to produce tortillas. Tortillas prepared by the traditional method just described generally show excellent rheological characteristics, such as puffing and elastic strength.
The major disadvantage of nixtamalization of whole kernel corn is related to alkaline waste and wastewater disposal. The cook steep liquor, nejayote, is an unavoidable by-product of the nixtamalization procedures and is a potential dangerous environmental effluent due to its composition and alkalinity. The proper disposal of the excess wastewater generated during nixtamalization is a major concern during commercial masa production, because wastewater discharge must typically meet specific regulatory requirements. As a result, methods of nixtamalizing corn that reduce effluent production would be both environmental and economically desirable.
Alkaline cooking, steeping and washing of corn also cause partitioning of corn in solids between the masa and the wastewater. Loss of corn solids (i.e., yield loss) during nixtamalization and effluent processing and clean-up costs are considerable. In a commercial operation, corn solids loss has been estimated to vary between 5 and 15% depending on the type of corn. The effluent generated (nejayote) is a potential pollutant because of its composition and characteristics. Nejayote is highly alkaline (pH 11-12), and its solids fraction contains about 75% nonstarch polysaccharides, 11% starch and 1.4% protein and high calcium levels. Nejayote has a chemical oxygen demand (COD) of about 25,000 mg/L, a biological oxygen demand (BOD) of 8,100 mg/L, and a suspended solids content of 20,000 mg/L. In addition to a high BDO and COD, nejayote contains nearly 310 mg of nitrogen and 180 mg of phosphorus per liter. Commercial alkaline corn processing facilities discharge alkaline wastewater in large sedimentation tanks or lagoons for disposal. Some operations dispose of some of the water by irrigating cropland or grass. Sedimentation and microbial degradation of corn solids accomplish wastewater-cleaning operations. Due to alkalinity, wastewater cannot typically be directly discharged into the environment or water streams before proper neutralization.
In large commercial establishments where efforts are focused on expending the nixtamalization process and minimizing steeping times, corn is usually cooked at high temperatures and quenched with water to rapidly reduce corn temperatures. Although this approach shortens process times, it can increase water use and, thus, increase wastewater volumes. A typical corn nixtamalization facility processing 200 tons of corn per day uses more than 50 gal of water per minute and generates nearly the equivalent amount of alkaline wastewater in a 24-hr period.
Research is being done to find effective, economical alternatives to alkaline waste disposal. One approach has been to remove the suspended solids from the wastewater steam by vacuum filtration and then use reverse osmosis to remove dissolved solids. Membranes used in this type of system retain nearly all solids and let only water pass through. However, these membranes are expensive.
In recent years, several processes have been developed for nixtamal, masa, and masa flour production. Many of these processes have been developed to shorten the cooking or steeping process or increase production rates. In one example masa flour production process, the whole grain is partially cooked in a hot alkaline solution to partially gelatinize the starch. The corn is then de-branded, flash-dried, and milled. Several processes use ground corn or corn flour as the starting material and use extrusion or continuous cooking to produce masa or masa flour. These procedures, however, have not completely overcome the waste-generation problems associated with the traditional masa production process. Problems related to product quality, equipment and process costs, and production rates are also sometimes encountered with processes using ground corn material (flour or meal) mixed with lime or using extrusion.
To partially overcome the problem in the quality of masa and tortilla some industrial producers of instant corn flour use gums such as carboxymethyl cellulose, guar, xanthan and Arabic gums to facilitate keeping properties and functionality in tortillas and helping to counteract the effects of lack of pericarp gums due to shorter steeping times during the cooking of corn grains. The flour producers remove the pericarp that affects the color of the products. However, tortilla manufacturers know that rehydrated dry masa flour has different rheological properties compared to fresh masa. Rehydrated dry masa flour is less plastic and cohesive than fresh masa. Also, the products made from dry masa flour stale faster. Similarly, the quality of the texture and flavor of tortilla made from instant corn flour is lower than that made from fresh masa.
Consequently, a need exists for a process for making masa that eliminates the lye steeping step, eliminates the discharge of caustic and wasteful effluent, shortens processing times, yet produces a masa that is rheologically similar to masa produced by the traditional nixtamalization process. Ideally, such process should be accomplished with minimal material costs and with equipment that is normally available to producers of fresh masa made by the traditional process. In short, the method should be economical, environmentally friendly, and produce an end product that is indistinguishable from the same type of product made by the traditional process.